1. Field of the Invention
The present invention relates to a linear light source used in a facsimile device or scanner and, more particularly, to an LED-array light source in which a number of LEDs (Light Emitting Diode) are linearly arranged as a light source for a contact-type image sensor.
2. Description of the Prior Art
Recently, an LED-array light source constituted by linearly arranging a number of LEDs is widely used as a linear light source for irradiating an original copy for a contact-type image sensor in an image reader for a facsimile device or scanner.
Since each LED of the LED-array emitts a directional light, it is necessary to linearly arrange a large number of LEDs to obtain uniform linear illumination. If LEDs are arranged in a pitch of 6.5 mm, illuminance distribution becomes substantially even on the surface of an original so that uniform linear illumination can be obtained.
In view of cost, it is desirable to reduce the number of LEDs as long as there arises no problem in uniform illuminance distribution for reading the original copy. However, if the number of LEDs is reduced so as to arrange them in, for example, a pitch of 16 mm, the illuminance distribution becomes uneven on the surface of the original. Japanese Unexamined Patent Publication (Kokai) No. 4-29379 proposes an LED-array light source which can reduce the number of LEDs.
As is shown in FIGS. 5(a) and (b), a number of LEDs 52 are arranged on an elongated printed circuit board 51 in a row, and sealed by transparent resin 53. A light adjusting mask 55 is provided on the sealing resin 53. The light adjusting mask 55 is made of a thin transparent film provided with shielding pattern 54 which intermittently shields the illumination light from the LED 52.
However, the shielding pattern 54 has a disadvantage that, because the shielding pattern 54 is intended to maintain uniformity for an area with low illuminance by reducing the illuminance at areas with higher illuminance so that the overall illuminance is significantly deteriorated and the efficiency in use of illumination light from the LED becomes low. In addition, the shielding pattern affects the illuminance distribution as a shadow so that it cannot provide sufficient effect in uniformity the illuminance distribution.
An object of the present invention is to provide an LED-array light source in which the number of LED devices is reduced, but the efficiency in use of illumination light is enhanced and uniform illuminance distribution is attained.